Fix InetAddress-wrapping of long AFSocketAddresses

Long socket addresses, such as non-ASCII addresses in the Abstract
Namespace close to the maximum length of 108 bytes may not be
representable by our custom address wrapping representation used for
InetAddress, resulting in an exception upon bind, etc.

This is caused by URL-encoding any non-printable characters, resulting
in three UTF-8 characters per byte (3*108+x > 255, an internal limit).

Introduce a fixed-length hex-encoding, which is recognizable by a
wrapped-hostname string starting with "[%%", followed by a sequence of
2-character hex values (2*108+2+x <= 255).

junixsocket-common/src/main/java/org/newsclub/net/unix/AFInetAddress.java

@@ -31,6 +31,7 @@
 import java.net.URLEncoder;
 import java.net.UnknownHostException;
 import java.nio.charset.StandardCharsets;
+import java.util.Locale;
 import java.util.Objects;
 
 /**
@@ -87,6 +88,7 @@ class AFInetAddress {
   };
 
   private static final char PREFIX = '[';
+  private static final String MARKER_HEX_ENCODING = "%%";
   static final String INETADDR_SUFFIX = ".junixsocket";
 
   /**
@@ -111,6 +113,23 @@ static final String createUnresolvedHostname(byte[] socketAddress, AFAddressFami
     } catch (UnsupportedEncodingException e) {
       throw new IllegalStateException(e);
     }
+    sb.append('.');
+    sb.append(af.getJuxString());
+    sb.append(INETADDR_SUFFIX);
+
+    String str = sb.toString();
+
+    if (str.length() < 64 || str.getBytes(StandardCharsets.UTF_8).length <= 255) {
+      return str;
+    }
+
+    sb.setLength(0);
+    sb.append(PREFIX);
+    sb.append(MARKER_HEX_ENCODING);
+    for (int i = 0, n = socketAddress.length; i < n; i++) {
+      sb.append(String.format(Locale.ENGLISH, "%02x", socketAddress[i]));
+    }
+
     sb.append('.');
     sb.append(af.getJuxString());
     sb.append(INETADDR_SUFFIX);
@@ -185,11 +204,26 @@ static final byte[] unwrapAddress(String hostname, AFAddressFamily<?> af) throws
     }
 
     String encodedHostname = hostname.substring(1, domDot);
-    try {
-      return URLDecoder.decode(encodedHostname, StandardCharsets.ISO_8859_1.toString()).getBytes(
-          StandardCharsets.ISO_8859_1);
-    } catch (UnsupportedEncodingException e) {
-      throw new IllegalStateException(e);
+    if (encodedHostname.startsWith(MARKER_HEX_ENCODING)) {
+      // Hex-only encoding
+      int len = encodedHostname.length();
+      if ((len & 1) == 1) {
+        throw new IllegalStateException("Length of hex-encoded wrapping must be even");
+      }
+      byte[] unwrapped = new byte[(len - 2) / 2];
+      for (int i = 2, n = encodedHostname.length(), o = 0; i < n; i += 2, o++) {
+        int v = Integer.parseInt(encodedHostname.substring(i, i + 2), 16);
+        unwrapped[o] = (byte) v;
+      }
+      return unwrapped;
+    } else {
+      // URL-encoding
+      try {
+        return URLDecoder.decode(encodedHostname, StandardCharsets.ISO_8859_1.toString()).getBytes(
+            StandardCharsets.ISO_8859_1);
+      } catch (UnsupportedEncodingException e) {
+        throw new IllegalStateException(e);
+      }
     }
   }
 

junixsocket-common/src/test/java/org/newsclub/net/unix/domain/AbstractNamespaceTest.java

@@ -82,4 +82,12 @@ public void testBindTrailingZeroes() throws Exception {
     // any sequence of 0's -> null
     testBind(AFUNIXSocketAddress.of(new byte[] {0, 0, 0}), null);
   }
+
+  @Test
+  public void testBindLongAbstractAddress() throws Exception {
+    byte[] addr = new byte[108];
+    addr[1] = '1';
+    addr[79] = 'X';
+    testBind(AFUNIXSocketAddress.of(addr));
+  }
 }